Photographic lens optical system

Abstract

A photographic lens optical system includes: a first lens having a positive refractive power and a meniscus shape convex toward an object side; a second lens having a negative refractive power and a meniscus shape convex toward the object side; a doublet lens having a positive refractive power and formed by combining a third lens and a fourth lens; a fifth lens having a positive refractive power and a double convex shape; and a sixth lens having a positive refractive power and a double convex shape. The first to sixth lenses are sequentially arranged in a direction from the object side to an image side, and the photographic lens optical system satisfies the following condition: 1.5< Nd 2<1.7 where Nd2 denotes a refractive index of the second lens.

What is claimed is: 
     
       1. A photographic lens optical system comprising:
 a first lens having a positive refractive power and a meniscus shape convex toward an object side; 
 a second lens having a negative refractive power and a meniscus shape convex toward the object side; 
 a doublet lens having a positive refractive power and formed by combining a third lens and a fourth lens; 
 a fifth lens having a positive refractive power and a double convex shape; and 
 a sixth lens having a positive refractive power and a double convex shape, 
 wherein the first to sixth lenses are sequentially arranged in a direction from the object side to an image side, and the photographic lens optical system satisfies the following condition:
   1.5 <Nd 2<1.7 
 
 where Nd2 denotes a refractive index of the second lens. 
 
     
     
       2. The photographic lens optical system of  claim 1 , wherein the doublet lens has a concave object-side surface. 
     
     
       3. The photographic lens optical system of  claim 2 , wherein the third lens is a double concave lens and the fourth lens is a double convex lens. 
     
     
       4. The photographic lens optical system of  claim 1 , wherein the photographic lens optical system satisfies the following condition:
   BFL/ f< 1.4 
 where BFL and f denote a back focal length and a focal length of the photographic lens optical system, respectively. 
 
     
     
       5. The photographic lens optical system of  claim 4 , wherein the doublet lens has a concave object-side surface. 
     
     
       6. The photographic lens optical system of  claim 5 , wherein the third lens is a double concave lens and the fourth lens is a double convex lens. 
     
     
       7. The photographic lens optical system of  claim 1 , wherein at least one lens of the photographic lens optical system is formed of a plastic material. 
     
     
       8. The photographic lens optical system of  claim 7 , wherein the second lens is formed of a plastic material. 
     
     
       9. The photographic lens optical system of  claim 8 , wherein the second lens has at least one aspheric surface. 
     
     
       10. The photographic lens optical system of  claim 1 , further comprising an aperture stop disposed between the second lens and the third lens. 
     
     
       11. A photographing apparatus comprising:
 the photographic lens optical system of  claim 1 ; and 
 an image sensor converting an optical image formed by the photographic lens optical system into an electric signal.